Filters can be used to reduce water consumption in a washing appliance for cleaning various articles, such as a dishwasher or washing machine, by extending the useful capacity of a working fluid by cleaning working fluid that has become entrained with various soils, debris, and other foreign particles that have been removed from the articles. The filter extracts soil from the working fluid, and the filtered working fluid can be recirculated and reused.
The majority of filters employed are conventional cake filters as shown in FIG. 1, which operate under the principle of size exclusion. However, cake filters can only filter a limited amount of working fluid before particles begin to accumulate on the surface of the filter, forming the cake. As the cake thickens, the pressure necessary for the working fluid to flow through the cake to the filter increases, which reduces and eventually destroys the cleaning ability of the cake filter.
An alternative to cake filtration is cross-flow filtration as shown in FIG. 2, which also employs the principle of size exclusion. Cross-flow filtration can comprise a three-port system where recirculating working fluid flows through the filter to clarify a portion of the working fluid. The working fluid flows in a direction tangential to the filter such that a portion of the working fluid flows across the filter and is then recirculated while another portion of the working fluid flows through the filter and exits as clarified working fluid. Some of the particles that lodge on the filter surface are carried off by the recirculating working fluid. However, shear forces produced by the working fluid flowing across the filter is not enough to remove all particles from the filter surface, and the particles build up and eventually clog the filter.